Preparation of cyclooctatetraene



Patented Oct. 7, 1952 Alfred'J. Canale, 'Moorestown, and John F.Kincaid, 'Mount Holly, N. J assignors to Rohm & Haas Company;Philadelphia, Pa a corporation of Delaware No Drawing; Application March9, 1950,

3 serial No. 148,734

' terials, and not truly reproducible. Forlthe practical preparation ofcyclooctatetraene it is almost essential that shortcomings anddifllculties of the art be corrected or avoided.

We have found that' cyclooctatetraene is formed at a relatively rapidrate and in a reproducible manner by tetramerizing acetylene-at 100 to600 p. s. i. by heating it in the presence of nickel monocyanide at 90to 150 0., preferably between 110 and 150 C. The nickel monocyanide iswet with a water-miscible organic solvent such as dioxane ortetrahydrofurane, and may be mixed therewith in amounts ofi0.1 part-byweight to 20 parts per 100 parts of thesolventl- In a preferred methodnickel monocyanideis prepared from K2Ni(CN)4 or' NazNitCNn by reductionwith potassium or sodium metal in liquid ammonia. A red precipitate,K2Ni(CN)s or the comparable sodium salt, is formed and is separated. Theprecipitate is dissolved in a minimum amount of air-free water and thissolution is poured with vigorous agitation into cooled (-15 C.)hydrochloric acid about normal in strength.

A precipitate of NiCN is formed and is separated, as by centrifuging.The solid is washed until free of acid with deaerated water which isthen displaced with a water-miscible solvent. Dioxane, tetrahydrofurane,and other water-miscible anhydrous organic solvents, which are alsouseful as solvents in the tetramerization reaction, are examples ofsolvents suitable for this purpose.

When the nickel monocyanide is used imme- 1 diately after preparation,"there is no induction period for formation of "cycloocctatetraene. Whenthe catalyst is aged, a short induction period is usually observed. Withnickel monocyanide as catalyst, the rate of tetramerization is manytimes that experienced with Ni(CN) 2. For instance, with nickelouscyanide under conditions of the art 4 to 5 grams per liter-hour wasfound to be the rate of tetramerization. When nickel monocyanide is usedat 115 C. under otherwise similar conditions except that the nickelteams." (ct'zso -sss) monocyanide is taken in-an amount which is onefifth of the weight of nickelous cyanide, the rate is grams perliter-hour.

Solvents" which are useful for wetting and suspending the nickelmonocyanide include not only dioxane and tetrahydrofuranewhich have beenmentioned but also water-miscible diethers of glycols, such as thedimethyl ethers of ethylene glycol, diethylene glycol, triethyleneglycol, tetraethylene glycol, propylene glycol, or dipropylene glycol,diethyl ethers of these glycols, mixed methyl and ethyl ethers thereof,and mixtures of the various diethers. Another type'of ether comprisesacetals, such as dibutyl acetal, dipropyl acetal, diethyl-formal,dibutyl formal, etc.

To themixture'of nickel-monocyanide and sol vent there may be addedpulverized calcium carbide. An amount from 0.5 gram to 5 grams per partsof solvent provides a satisfactory range.

The calcium carbide reacts with any water which may be present inthe'nickel monocyanide after solvent has been added thereto. The calciumliydroxide'which then results can take up any trace of acid which mighthave been left in the catalyst. The use of calcium carbide thus permitsa less critical washing of the nickel monocyanide and displacement ofwater by solvent. Aft er thorough washingwith water and repeated rinsingwith solvent the use of calcium carbide is'not essential even thoughthere appears to be some slight advantage in ensuring alkalinity, as byits use. 7

Acetylene is used under pressures of 109 to 606 pounds per square inch.The reaction is desir ably initiated at the lowest practical pressureand then the pressure may be increased. A range of 300 to50O pounds persquare inch for the partial pressure ofthe acetylene is preferred.Precautions for handling acetylene have ben described at length in theart. Essential precautions include use of narrow tubes and/or dilutionwith inert gas or vapor.

In carrying out the tetramerization of acetyl ene a pressure vessel mustbe used. It is charged with aimixture of catalyst and solvent. Thevessel is swept out with an inert gas such as nitrogen to displace air.The inert gas may be displaced with acetylene before or after heating.The charge of catalyst and solvent is heated to 90 to C. and acetyleneis run in slowly at gradually increasing pressure. It is desirable toinitiate the reaction at a relatively low pressure. Too rapidapplication of pressure may sometimes cause an explosion. After reactionhas started, pressure can be increased. Acetylene is pressuredoctatetraene by the method of this invention" will be found in thefollowing illustrative erg,

amples Example 1 of freshly prepared nickel monocyanide, 5 parts ofpulverized calcium carbide and Q parts oi anhydrous dioxane. This slurrywas placed troduction from time to time of acetylene at 500 p. s. i.After 2.5 hours the reaction was interrupted by cooling the bomb to 25C. and venting the acetylene. The reaction mixture was distilled at onemm. pressure. No polymeric lay-products were here obtained as residue.The :distillatefwas. washed with water, separated, dried, andfractionally distilled. There were obvitytained 9 grams ofcyclooctatetraene and 2.5 .1

rams of benzene.

The above examples illustrate typical procedures for. preparingcyclooctatetraene by the I v if .'-process of this invention. Theprocess is char- A slurry was prepared from 0.5-part byv weightact'rized by positive, dependable production of the desired product. Itdepends upon contactingv acetylene under pressure with nickelmonocyanide between 90 and 160 0., preferably in a. high pressure rockerbomb which was sealed,

swept with nitrogen, and heated to-'1l5-"C.

Acetylene was slowly admitted. Gas absorption began immediately.Gradually thepressure of acetylene was raised to 500 p. 5. iiandmaintained between 300 and 500 p. s. i. by occasional introduction ofacetylene. The acetylene was taken from a cylinder, passed voveractivated charcoal to remove acetone vapors, and, over activatedalumina, compressed, and run into the bomb as needed. After two hoursthe preparation was discontinued. The bomb was cooled and the acetylenevented. Thejreaction mixture was distilled at one -mm. pressure. Thedistillate was washed with water to remove dioxane. The organic layerwas separated, dried over calcium chloride, and distilled. There wereobtained 6 parts by weight of benzene and 14 parts of cyclooctatetraene.Some polymeric material was obtained as a residue in thefirst'distillation.

. w r e Z Nickel monocyanide was prepared by dissol ing 6.7 grams ofKzNi CN in 400 ml. of liquid ammonia, adding 0.5 gram of metallicpotassium in small portions to form a red precipitate, de-

canting ofi the ammonia, taking up ,the red precipitate of K2Ni( CN) ain water which had been boiled to free it of air, acidifying theresulting solution with 5 N hydrochloric acid .cooled to 15 C., andseparating and washing the resulting NiCN with deaerated water.-While-this product could have been used as in Example hit was storedunder water for hours before use. The water was decanted from the nickelmonocyanide which was then washed several times with dioxane.

A slurry was made with 0.5 gram of the aged nickel monocyanide, 5 gramsof pulverized calcium carbide, and 100 parts ,of'anhydrous dioxane. Theslurry was placed in a high pressure rocker bomb, which was sealed,swept out with nitrogen, and heated to 115 C; Acetylene was slowly runinto the bomb to a pressure of 500 p. s. i. After about 20 minutes thetemperature of the charge began to rise, indicating that an exothermicreaction had started. Acetylene absorption began at this time. Thepressure was maintained between 300 and 500 p. s. i. byinthe presence ofa high boiling, water-miscible anhydrous solvent. The ether solvents areparticularly desirable. Calcium carbide may be added to ensure ananhydrous state and react with any acid which might'have been left inthe nickel monocyanide catalyst. When the catalyst has been stored underwater prior to its'use, there appears to be little tendency forthe'formation of polymeric residues.

l. A process for preparing cyclooctatetetraene which comprisestetramerizing acetylene by contacting it withnickel monocyanide at to150 C. under a pressure of to 600 pounds per square inch.

2. A process for preparing cyclooctatetraene which comprisestetramerizing acetylene by contactingit with nickel monocyanide in thepresence of a high boiling water-miscible anhydrous organic solvent atto C. under a pressure of 300 to 500 pounds per square inch.

' 3. A process for preparing cyclooctatetraene which comprisestetramerizing acetylene by contacting it with nickel monocyanide in thepresence of calcium carbide and of a high boiling water-miscibleanhydrous organic solvent at 110 to 150 C. under a'pressure of up to 500pounds per'square inch.

4'. A process for preparing cyclooctatetraene which comprisestetramerizing acetylene by contacting it with a nickel monocyanidecatalyst in the presence of calcium carbide and of a high boiling watermiscible anhydrous ether solvent at 110- C. to 150 C. under an acetylenepressure of 300 to 500 pounds per square inch, the said catalyst havingbeen stored under water prior to its use into the reaction mixture.

' ALFRED J. CANALE.

JOHN F. KIN'CAID.

REFERENCES CITED

1. A PROCESS FOR PREPARING CYCLOOCTATETETRAENE WHICH COMPRISESTETRAMERIZING ACETYLENE BY CONTACTING IT WITH NICKEL MONOCYANIDE AT 90*TO 150* C. UNDER A PRESSURE OF 100 TO 600 POUNDS PER SQUARE INCH.